Means for varying the electrical impedance of a circuit



Dec. 6, 1927;

' v E, R. STOEKLE MEANS FOR VARYING THE ELECTRICAL IMPEDANCE OF A CIRCUIT Filed Nov. 24, 1924 63' MW M INVENTQR:

Patented Dec. 6, 1927.

UNITED STATES ERWIN B. STOEKLE, OF IMILWAUKEE, WISCONSIN.

MEANS FOR VAR'YING THE ELECTRICAL IMPEDANCE OF A CIRCUI'I..-

Application filed November 24, 1924. Serial No. 751,911. 1

Method of and means for varying the elecri'ical impedance of a circuit.

This invention relates to an improved method and means for varying the electrical e impedance of a circuit particularly for varying the so-called reactive or inductive component of said impedance.

In electrical circuits, especially of the t e employed in radio communication it iso ten desirable to adjust the relation between the inductance and the resistance of a circuit with great accuracy. For example the conditions under which a vacuum tube will oscillate is governed by the relation estab- 35 lished between the external and the internal impedance of the tube. The condition for self-oscillation of the tube is usually expressed by stating that the inductance in the plate circuit of the tube must be sufficient to effect complete neutralization of the-circuit resistance. Although the devices to be herein described are particularly adapted to the control of oscillation and the tuning of vacuum tube radio circuits they are applicable to any electrical circuit the impedance of which is desired to be controllably varied.

One object of this invention is to provide an improved method of varying the electrical characteristics of a circuit particularly the inductance thereof.

Another object is to provide improved means for varying the relation between the inductance and the resistive component of the impedance of a circuit.

Another object is to provide improved means for varying the phase relation between the currents and the magnetic fluxes in two or more coils placed in mutually inductive relation to one another.

Another object is to provide improved means for changing the inductive component of the impedance of an electrical circuit by changing the resistive component of the circuit.

Another object is to provide improved means for controlling the conditions governing the oscillation of electrical circuits including so-called three element vacuum tubes.

Other objects and novel features of this invention will be apparent from the following specification and the accompanying drawings. v

In the drawings;

Fig. 1 shows a wiring diagram-of a preferred form of the invention.

Figs. 2 and 8 show two methods of effectgreater part going through coil point 1. Let

ing the necessary movements of the contacts upon the resistors, by a single operating means.

Fig. 4 shows a wiring diagram of another form of the device, and Fig. .5 the corre sponding method of carrying outthe necessary movement of the contact arm on the resistor. I

Fig. 6 shows a form of the device in which a simple rheostat is used to vary the self,- induction of two mutuallyinductive coils.

Fig. 7 shows a form of the device in which the mutually inductive coils are connected electrically in parallel and regulation of the division of current between fected by means of a so-called potentiometer resistance.

Referring to the Fig. 1 the device shown is to vary the impedance between the points 1 and 2 at which points it may be connected in an electrical circuit whose characteristics are to be controlled. The resistances 3 and 4 are connected electri ally in parallel by means of the conductors 5 and 6. -The inductance coils 7 and 8 are placed in mutually inductive relation to one another, that is the magnetic fiuxof coil 8 must link with the turns of coil 7. This interlinkage of flux between the coils 7 and 8 should be preferably although not necessarily as great as possible, so that the relation of the coils will be that which is commonly referred to as close coupled. The conductors?) and lO (Fig. 1)

are adapted to make contact at a variable location on the resistances 3 and 4.

The operation of this device is as follows:

The impedance of the device as measured between the points 1 and 2 is a function of. the resistances? 1' 7' and r, and of the self and the mutual inductances of the coils 7 and 8. Let us first consider the case when the conductor 9 makes contact at the extreme ri 'ht end of resistance 3, adjacent conductor 6 gand conductor 10 makes contact at the ex-' treme left end of. resistance 4. Under these conditions r =r =O and r 'is the entire re,-

sistance of 3 ,while 1', is the entire resistance of 4. Current enteringhat-the point 2 will pass through coil 8 to e point 11. At this point it will divide. into three parts; the 7- while the remainder divides between the resistances 3 and 4. These three currents recombineat and leave the device atthe us also assume that the wind- 7 and 8 are such thatwith the the point 12,

ings of coils the coils is efinductive coils in above described distribution ofcurrent the maetic flux due to the current in coil 7 is adci d to the flux due to the current in coil 8. This results in a maximum of self-induction between the points 1 and 2 of the device.- It will be noted that under these conditions the device substantially comprises two mutually series, one of. them namely the coil 7 being electrically in parallel with the resistances 3 and 4. If the resistances 3 and 4 are very large relative to the impedance of coil 7 the resultant inductance between the oints 1 and 2 will be given approximately by the expression:

L==L,+L +2M.

Where L is the self induction of coil 7, L is the self induction of coil 8 and M is the mutual inductance'of coils 7 and 8.

Let us now consider the case when the conductor 9 makes contact at the extreme left end of resistance 3, and the conductor 10 makes contact at the extreme right end of the resistance 4. It is apparent that under these conditions the device again substantially comprises a series connection of the mutually inductive coils '7 and 8 with the coil 7 electrically in parallel with resistances 3 and 4. Thereis, however, an essential difference between the last considered case and that first considered in that the current in coil 7 has been completely reversed. This results in a reversal of the flux in coil 7 so that instead of being added to the flux of 'coil 8 it is subtracted therefrom. This case therefore gives a minimum of self-induction between the points 1' and 2 the approximate EXPIGSSIOII for the resultant self-induction If the coils 7 and 8 be very closely coupled the mutual inductance value /L L then it is apparent that L would approxi- If the coils 7 and 8 are so wound that If the resistances 3 and 4 are enough to divert a negligible current tance it is desirable to wind more turns on self the coil' 7 than are on the coil 8. The above discussion shows that a maximum limit of inductance determined by the and mutual inductances of the coils 7 and S may be'obtained and a minimumlimit approaching zero may also be obtained these limits corresponding. to the two diagonally M approaches the opposite positions of the contacts on the resistances 3 and 4. Values of inductance intermediate these limits may be obtained by intermediate positions of contacts of conductors 9 and 10 upon their respective resistances 3 and 4. Reversal of the current in the coil 7 Will take place at contact positions near the central portions of resistances 3 and 4.

These represent the contact positions at which the magnetic fluxes of coils 7 and 8 change from additive to subtractive relations, with correspondingchanges in the resultant inductance of the device. The changes in inductance above described can allbe accomplished in a gradual and continuous manner by a gradual change of the location of the contacts of conductors 9 and 10 upon their respective resistances 3 and 4.

The Fig. 2 shows a form of the device in which the above described changes in inductance can be brought about by a single operating means. Referring to F ig. 2 the terminals of the device are shown at 13 and 1 1. Resistances 15 and 16 are circularly disposed on an insulating base 17 and provided with suitable common terminals 18 and 19. The contact members 20 and 21 are adapted to make contact respectively with the resistances 15 and 16 and are connected to the ends of coil 28 by means of conductors 24 and 25. These contact members 20 a d 21 are fixed to the shaft 26 in such a way-as to be electrically insulated from one another. The shaft 26 extends rotatably through the base 17 and may be rotated by means of the operating knob 27. The mutually inductive coils 28 and 29 of Fig. 2 correspond to the coils 7 and 8 of Fig. 1.

The operation of the device is-as follows:

Current entering at 14 passes through the coil 29, thence to terminal 19 from which it divides between the resistances 15 and 16, and the coil 28, recombining again at terminal 18 and leaving the device at terminal 13.

The contact members 20 and 21 being electrically connected to conductors 24 and 25 to which the coil 28 is connected, permit of varying the connections of coil 28 to the resistances 15 and 16 by rotation of the operating knob 27. When contact member 20 is adjacent terminal 19, member 21 is adjacent terminal 18. Thisposition of the contact members corresponds to the case discussed under Fig. 1 in which conductor 9 (Fig. 1) made contact at the ri ht end of resistance, 3 and conductor 10 made contact at the left end of 4. It is, therefore,

apparent that a 180 degree rotation of the knob 27 effects gradual change of the resultant inductance between terminals 13 and 14 over a ran e extending between the limits discussed in connection with Fi 1.

Fig. 8 shows form of the device in which adjustment from maximum to minimum inductance is accomplished by asingle operating means rotatable through an angle of approximately 300degrees. This makes possible a closer adjustment of the inductance than With the device of Fig. 2.

' Referring to the Fig. 3 the resistances and 31 circularly disposed on the insulating bases 32 and 33 correspond-to the resistances 3 and 4 of 1. Terminals 34, 35, 36 and 37, 38, 39 are provided tomake electrical connection to these resistances. 'Terminals- 34 and 37 and and 39. are' interconnected by the conductors 40 and 41 in order to give theyconnecti-ons shown diagrammatically in Fig. 1. The contactmenibers 42 and 43 are electrically insulated from each other and .fixed to the common shaft44. This. shaft ductor 40 and leaves the device at the terminal 47-. Fig. 4' shows diagrammatically a' somewhat modified device for changing the relation of the magnetic fluxes in two mutually inductive coils and thereby changing the resultant self induct-ion of these coils. In this figure a current. enteringatterrninal 51 passes through the coil 53 and the resistance" 52. One end, of the 'coil is connected througha resistance 55 to an intermediate point- 57 on the resistance 52, and the other I end is connected. to a conductor '56 adapted to-make contact at a ;.variab le' location on resistance 52. It is apparent that when the conductor 56 makes contact to the left. of the point 57 .the current in coil 54 will flow in a direction opposite to that in which it will flow when conductor '56 makes contact to the right of point 57 Itis also apparent that the amount of current flowing in coil 54 will be a function, of the position of contact of the conductor 56 upon the resistance 52. It, therefore, follows that a variation of the location of the contact of 56 upon resistance 52 will effect a variation both in the magnitude of the magnetic flux of 54 and in the relation of this flux to the flux of coil 53.

This variation of flux will'result in a variation of the resultant self induction between the terminals 50 and 51.

Fig. 5 shows how the necessary variation of contact described for Fig. 4 maybe accomplished by a single operating means.

Referring to Fig. 5 the resistance 58 corresponds to resistance 52 of Fig. 4; coils 59. an

60 correspond to-the coils 53 and 54 of through the coil 49 correspond-- Fig. sistance 55 of Fig. 4. The rotatable contact member 62 fastened to the shaft 63 corre-.

sponds to the movable conductor 56 of Fig. 4. It is apparent from Fig. 5 that rotatiorrof the operating knob 64 changes the location of contact of the member 62 over' the full range of resistance 58 thus accomplishing.

the desired changesof resultant inductance ofthe-coils 59 and 60.

Fig. 6 shows another modification for varying the resultant self-induction of two mutually inductive coils by changing the relation of their magnetic fluxes by means of a variable resistance. Referring to Fig. 6 current entering at the terminal 65 passes through'the coil 67 and then divides part passing through coil 68, the remainder being shunted around coil 68 through the variable resistance 69. The current leaves the device at terminal 66.

The variable resistance may be of the usual type comprising a contact memberbearing on the resistance, 69 and rotatable by a'knob 71, butpreferably should be of the non-inductive type such for instance as described. in my co-pending application SerialNumber 634,297.

-The coils 67 and-68 are preferably very closely coupled and so wound and placed with respect to each other that the magnetic flux of coil 68 opposes the fiux of coil 67.-

Assuming these coils to have the same self- 4 and resistance 61.cor1esponds to reinduction and to be perfectly closely coupled the resultant self-induction of the coils will approach zero at the value of the resistance 69 approaches infinity. Also as the value of the resistance 69 approaches zero the resultant self-induction of the coils will approach that of coil 67 alone.

The last described form of the device although the simplest does not give as great a range of variable inductance with two given'coilsas do the forms of the device shown in the Figs. 1 to 5 inclusive. This is because in'the 'form shown in Fig. 6 the magneticfiux of coil 68 can be either added toor subtracted from the flux of coil 67 but can not be both added to and subtracted.

from the flux ofcoil 67 by the movement of a-single operating means. In the forms of the device shown in Figs. 1 to 5 inclusive rotation of the operating knob over part of the range adds the fluxes of the two coils and over the remainder subtracts. these fluxes. This is obvously a more effective use of the coils although it adds somewhat to the complexity of the resistance portion of the device.

A further form of the device in which th mutually inductive coils are connected electrically in parallel is shown in the Fig. 7. The mutually inductive coils 72 and 73 are so wound and placed with respect to one another that their magnetic fluxes mutually oppose. Current entering at terminal 75 is divided between the coils 72 and 73 by a socalled, potentiometer resistance 76; and the currents passin through the coils 72- and 73 recombine and eave the device at 74t. The distribution of current between the coils 7 2 and 73 determines the resultant self-induction of these coils. When the contact member 77 is adjacent'on-e terminal of the resistance 76 the current will be a maximum though the coil connected to said terminal and the resultant inductance will be substantially equal to that of said. coil. At some intermediate position of the contact member 77 the current will be so divided between coils 72' and 73 as to make the resultant of their magnetic fluxes approach zero in which case the resultant inductance of the device will be a minimum. This intermediate position will be determined by the relative selfinduction of the coils 72 and 73, as well as by their mutual induction. It is, therefore, apparent that rotation of the contact member by means of its operating knob 78 will effect a gradual change of the resultant inductance from a minimum value to the value of tzhe inductance of either of the coils, 72 or 3.

In the above described devices it is preferable but not necessary to employ resistances in which a gradual and continuous variation of the location of contact can be accomplished. Resistances of this type are described in my co -pending application Serial Number 634,297.

While several forms of the invention have been shown and described, these have been selected merely for purposes of illustration arid not in any way as limiting or restricting the invention which, as will be appreciated, may take a great variety of different forms and arrangement of parts without in any way departing from the spirit or scope thereof as defined in the ap ended claims.

What I claim as new an desire to secure by Letters Patent is: i

1. The combination of a pair of inductive- 1y related coils, a pair of terminals, one end of one of said coils being connected one of said terminals, the other end of said coil being connected .to the other terminal throu h a variable resistance and through the ot er of saidcoils, whereby the effective resultant inductance between said terminals may be varied.

2. The combination of a pair of inductively related coils, a pair of terminals, one

end of one of'said coilsfbeing connected to one of said terminals, the other end of said coilbeing connected through a reslstance to the other of said terminals, the ends of the other coil being connected to said resistance,

Y one ofthe connections being movable along said resistance.

3. The combination of a pair of resistances connected in parallel, a terminalconnected to one of the common points of said of one of said coils being connected to one.

of said terminals, a resistance connected to the other terminal and to the other end of saidvfirst mentioned coil, the otherof said coils having its ends connected to said resistanoe, one of the last mentioned ends being'connected to said resistance by means of a movable member, means for moving said member, whereby the 'efiective resultant inductance between varied.

5; The combination of a pair of inductive ly related coils, a air of terminals, one end of one of said coi s being connected to one of said terminals, theother end of said coil being connected through a resistance to'the other of said terminals, the ends of the other coil being connected to movable members electrically connected to said resistance, and.

a single control for simultaneously moving each of said. members to thereby vary the points of contact with said resistance and the resultant inductance between said terminals.

6. The combination of a pair of resistances connected in parallel,-a terminal con-' nected to one of the common points 'of said resistances, a second terminal, a. coil connected between the other common point of said resistances and-the second terminal, a second coil having its ends connected to.

said terminals may be movable members electrically connected to said resistances, and a single control means for si gultaneousl .movm said members to varv i e points 0 connect on of the ends of said second mentioned coil with said resistances, whereby the eflective resultant inductance may be varied.

7. A pair of inductively related coils electrically connected to jointly iconductively carry a high frequency current, and a variable resistance connected to said coils tovs. the distribution of sai coils, whereby the of said coils is varied.

- In witness whereof, I have" hereunto subcurrent through scribed my' name. y

- ERWIN.R.'STOEKLE.

resultant inductance 

